Printing matrix or mold component formed from an aminoplast resin-polyvinyl alcohol reaction product

ABSTRACT

A shapeable matrix is provided for use in making of graphic art reproductions and in particular as a mold in forming of printing plates and other marking items.

BACKGROUND OF INVENTION

1. Field of Use

While the invention is not limited to any particular field it hasspecific utility in the production of printing plates, pattern platesand other marking and shaping items.

2. Description of Prior Art

In the newspaper industry, for many years printing plates have been madeof lead formed against a matrix of wood pulp, clay and water.

Recently, to expedite printing plate duplication, plastic printingplates have been tried on a limited scale in place of the lead plates.In one process, a magnesium metal master or pattern plate is prepared bya photographic and etching process. A negative (or matrix) is thenformed by pressing a plastic against the metal to form a reproduction(negative) of the master plate. The plastic matrix is then used toproduce a number of "positive" copies for the actual printing functionwhen multiple press operation is employed. The copies ("positives") areformed by molding or pressing thermoplastics or rubber elastomersagainst the "negative" matrix.

In another process, instead of the metal "master" an organic plastic"master" or pattern plate is made using a liquid polyester polymer whichis cured by transmitting ultra-violet light through a photographicnegative or transparency of the printed format. In the areas struck bythe ultra-violet light, the resin is hardened. In the areas "screened"from the ultra-violet light, the resin remains liquid and is washed awayby an aqueous developing solution.

The polyester master or "positive" is then used as described above as asubstitute for the metal master to make a "negative" matrix which inturn can be used to produce multiple "positive" copies. The copies arethen used as the actual printing plates. (A process using the polyesterconcept is sold by Hercules Incorporated, Wilmington, Del. under thetrademark "Merigraph".)

However, the above prior processes have inherent deficiences as thematrix plates (negative plates) have been susceptible to taking acompression-set on repeated uses. As a result, the printing plate copiesor duplicates made from the negative matrix have letters of differentheights. The printed copy is thus blurry, smudged, and hard to read.Certain areas might have too much ink and others too little.

One conventional matrix concept uses a non-dense core of anasbestos-cellulose composition which has a phenolic resin coating.However, when a moldable material such as polypropylene is moldedagainst the matrix, the core gradually flows and compresses in thicknessproviding uneven print characters. Moreover, the phenolic resin of thematrix is susceptible to flex-cracking and peeling from the corematerial.

Other problems have been inherent with the prior phenolic-type matrixplates. When formed against the organic polyester "masters", thepressures required to form the phenolic "negative" matrix have causedthe print or characters on the organic polyester to collapse. Thephenolics also have a tendency to stick and bond to the polyester. Inaddition, the phenolic matrix plates cannot be bent easily to the curvedsurface of a mold platen (having substantially the same diameter as aprinting press cylinder) without cracking.

SUMMARY OF INVENTION

The present invention overcomes the deficiences of the prior art byproviding a matrix which can be used against either metal or plasticmasters to receive very sharply defined impressions. The imprintedmaterial then serves as a mold against which a plastic material ismolded to form multiple "positive" duplicates for use as the actualprinting plates.

For this purpose, the matrix must be capable of becoming dense whencured so that it will not take a compression-set when hot moltenplastics under pressure are molded against it; it must be flexible sothat it can be shaped to take the contour of a printing press drum orcylinder without cracking; it must have good release properties fromother plastics, particularly the polyesters, without bonding, stickingor distorting; it must be porous during its initial forming to allow forthe expulsion of air and gases; it must be capable of being moldedagainst a "master" (such as the polyesters) under relatively lowtemperatures and pressures so as not to cause the images and charactersof the master to collapse and flow laterally and it must be able towithstand the molding thereagainst of other plastics such as thepolypropylenes without taking lateral and vertical flow compression-set.The present invention accomplishes the foregoing by means of a novelmatrix which includes an amino-plast-polyvinyl alcohol product.

DESCRIPTION OF DRAWINGS

FIG. 1 is a plan view showing a matrix in sheet form prior to shaping ormolding.

FIG. 2 is an exploded side view showing the matrix of FIG. 1 beingplaced between molding platens for forming against a "master"("positive") printing plate.

FIG. 3 shows the matrix, after forming in FIG. 2, bent or deflected to acylindrical curvature and used as a part of a mold against which aplastic material can be injected in the making of multiple "positive"printing plate copies.

FIG. 4 shows a "positive" duplicate printing plate after molding to thecurvature in FIG. 3 mounted on a printing press cylinder.

DESCRIPTION OF INVENTION

While the invention has many applications, it will be specificallydescribed with reference to its application in the forming of printingplates and similar articles.

As shown in FIG. 2, a matrix sheet 10 of the invention is shaped orformed under heat and pressure against a "master" ("positive") printingplate 11 mounted in a molding press shown generally at 12. The press isshown schematically to have a top platen 13 and a lower platen 14.

The master ("positive") printing plate 11 is used as a pattern and maybe of metal such as magnesium or of plastic such as polyester. The sheet10, which contains a moldable resin (as will be described in detaillater) is then formed or molded by closing of the platens 13 and 14.Shaping is done at pressures of 20 to 200 psi and preferably in therange of 50 to 200 psi at temperatures generally between 225° F. to 370°F. depending on the material of the master 11.

After curing, the "molded" negative matrix (shown at 10' in FIG. 3) maythen be bent or curved to approximate the curvature of a printing presscylinder and inserted in an injection molding press shown schematicallyat 15 (FIG. 3) having a top plate 16 and a bottom platen 17. In thisview, the molded matrix negative 10' is shown curved and cradled in thebottom platen 17 with the imprinted image 18 thereon on the concave orupper side of the bend. The top platen 16 is then moved into clampingengagement relative to the bottom platen 17 as shown by the dotted lineposition.

After the top platen 16 is moved into the dotted-line position, aduplicate "positive" printing plate may be made by molding a plasticmaterial against the curved negative matrix 10'. As shown in FIG. 3,polypropylene or the like may be injected through the sprue opening 19into a relief cavity 20 in the top platen 16 overlying the molded matrix10' to make a duplicate "positive" printing plate 21 (FIG. 4). Theduplicate printing plate 21 upon molding has the curvature of the moldbase 17 so as to substantially match the curvature of a printingcylinder 22. As will be noted in FIG. 4, the duplicate plate 21 has itsprinting images or characters 23 on the convex side of the plate andthereby correspond with those of the master plate 11.

Now in accordance with the invention, in order to provide multiple"positive" copies or duplicates without showing any creep or compressivedeformation under successive moldings, the formed matrix 10' must bedense and homogeneous. In prior concepts, the matrix would compress andsuccessive positive duplicates would vary in thickness. This resulted inuneven printing effects because of the variation in the relief depth ofthe print characters.

To accomplish these requisites, in its broadest aspect, the presentinvention includes the reaction of the components of an aminoplastsystem with polyvinyl alcohol in the range of from 0.75 to 2.6 parts byweight of the aminoplast to 1 part by weight of polyvinyl alcohol, witha preferred range being 1.0 to 1.5 parts of the aminoplast to one partof polyvinyl alcohol. As is well known, the aminoplasts are syntheticresins of the thermosetting type which are prepared by reacting anorganic compound containing an amino group with an aldehyde or ketone.Typical of the amino group are urea, thiourea, cyclic ethylene urea,dicyandiamide, melamine, and alkyl and aryl melamines.

The molecular weight of the polyvinyl alcohol can vary between 2,000 to120,000. However where lower molding pressures are required, a polyvinylalcohol with a molecular weight range of about 2,000 to 14,000 has beenfound very desireable. The polyvinyl alcohol is available in variouspercentages of hydrolysis, and for some of the lower or medium pressuremolding applications, a polyvinyl alcohol with a 60% to 70% hydrolysisand a molecular weight in the range of 2,000 to 4,000 produces optimumflexibility and release with good compression-set resistance.

As for the preparation, the aminoplast-polyvinyl alcohol product can beprepared with conventional equipment. A typical sequence involves mixinga constituent from the amino group and an aldehyde or ketone, adjustingthe pH of the mixture in the range of about 7.5 to 9 and refluxing untila drop of the mixture hydrophobes (precipitates) in an excess of waterat approximately 0° C. The polyvinyl alcohol is then added and thereaction continued at reflux or at a suitable reaction temperaturegenerally in the range of 180° F. to 220° F. for a suitable length oftime. The reaction product may then be dehydrated to produce a fusiblepartially water soluble product. The dehydrated product may then becured to an insoluble infusible form by heating at temperatures in thegeneral range of 225° F. to 390° F.

As an ideal matrix, the sheet 10 may be made by applying theaminoplast-polyvinyl alcohol resin (combined with suitable well knownfillers and lubricants as will be described later) to a non-woven orsemi-porous carrier such as a glass fiber mat. The mat may then behandled easily and contain a predetermined amount of resin. Excellentresults have been obtained using a resin content of at least 85% byweight to 15% by weight of the porous carrier with optimum results beingapproximately 90% by weight of the resin to 10% by weight of thecarrier.

After the mat is cured in a mold 12 (FIG. 2), a matrix 10' is formedwhich is flexible and pliant and enables it to be bent or shaped for useas a mold insert 10'. In addition to being resilient and pliant, thematrix 10' in accordance with the invention has superior releaseproperties from polypropylene and other printing plate materials whichare molded against it. This is extremely important for print fidelityand definition since slight bonding or sticking to the matrix 10' cancause the print character to smudge or blurr.

In this context, for many newspaper printing operations the ability toproduce many "positive" plate copies is extremely important because ofthe number of presses required to run the same format concurrently tomeet high volume circulation requirements. The present invention thusprovides a means of quickly making duplicate printing plates (positives)economically out of thermoplastics such as polypropylene and the likewhich may be recycled by regrinding and remelting after they are used.

Typical examples of the invention for purposes of illustration only andnot for purposes of limitation follow.

EXAMPLE I

Mix 125 parts by weight of melamine with 200 parts of Formalin (37% CH₂O--formaldehyde) and adjust the pH of mixture to 8-9. Heat the mixture,maintaining this pH at reflux until a drop of mixture hydrophobes(precipitates) in an excess of 0° C. water. At this point 150 parts byweight of polyvinyl alcohol with a commercial molecular weight range of2000 to 4000 is added and reaction continued for 40 minutes at reflux.The reaction product is then dehydrated, preferably with vacuum toproduce a white fusible, partially water soluble product. From thisproduct, thirty-five parts (by weight) thereof are mixed with 5 parts ofCarbowax (as a hot melt processing aid), 1 part of zinc stearate(lubricant), 1 part of pigment for color and 51 parts of Wollastonitefiller (calcium silicate), and 5 parts of water as a processing aid.This resin filler mixture is then applied by hot melt processing to aglass mat so as to result in an uncured matrix prepreg of 90% resinmixture (by weight) and 10% glass mat approximately 0.075" thick. Theresultant uncured matrix is then utilized to make a cured matrix(negative) plate approximately 15"×24"×0.075" by molding and curing at325° F. and at 100 psi against a magnesium or polyester "master" plate.

The resultant matrix produced by pressing and curing themelamine-polyvinyl alcohol prepreg against the polyester "master" plateshowed exceptional release qualities from the polyester as well asexcellent flexibility. (If a conventional matrix of the phenolic coatedasbestos-cellulose core is used against a polyester master, excessivestreaking results making an unacceptable matrix.) The cured matrix plateof the invention was utilized as a mold insert in an injection moldingmachine and bent to an arc generated by an approximate 15" diameter asused on printing press cylinder. Polypropylene was then injection moldedagainst the matrix to produce duplicate "positive" printing plates. Thereproduction of the print from the polypropylene duplicate plates wasexcellent.

EXAMPLE II

React 120 parts of urea (2.6 moles approx.) and 325 parts (4 molesapprox.) of Formalin (37% CH₂ O formaldehyde) at reflux temperature for30 minutes a pH of 7. At this point add 125 parts of polyvinyl alcoholand continue heating for 30 minutes. This product is dehydrated to afusible powder and then mixed with 50 parts silica filler, one partglycerol monostearate lubricant, 5 parts of Carbowax, 1 part pigment and4 parts water. The mixture is applied to a glass mat carrier in theratio of 25 parts resin mixture to 15 parts glass to give a matrixprepreg. The matrix is utilized to make a plastic "negative" printingplate by molding against a Merigraph polyester master at 100 psi and300° F.

EXAMPLE III

Mix 125 parts by weight of melamine with 200 parts of Formalin (37% CH₂O--formaldehyde) and adjust the pH of mixture to 8-9. Heat the mixture,maintaining this pH at reflux until a drop of mixture hydrophobes(precipates) in an excess of 0° C. water. At this point 75 parts byweight of polyvinyl alcohol are added and reaction continued for 40minutes at reflux. The reaction product is then dehydrated, preferablywith vacuum to produce a white fusible, partially water soluble product.From this dehydrated product, thirty-five parts (by weight) thereof aremixed with 5 parts of Carbowax (as a hot melt processing aid), 1 part ofzinc stearate (lubricant), 1 part of pigment for color and 51 parts ofWollastonite filler (calcium silicate), and 5 parts of water as aprocessing aid. This resin filler mixture was then applied by hot meltprocessing to a glass mat so as to result in an uncured matrix prepregof 90% resin mixture (by weight) and 10% glass mat.

The resultant matrix was then utilized to make a plastic "negative"printing plate by molding and curing at 325° F. and 100 psi against apolyester "master" or "positive" plate (as in Example I).

This formulation was generally unsatisfactory for the production ofduplicate printing plates as cracking occurred when the cured matrix wasbent to the approximate 15" diameter to be used for a printing platemold insert (against which it was desired to mold a polypropyleneduplicate "positive" printing plates).

EXAMPLE IV

Mix 125 parts by weight of melamine with 200 parts of Formalin (37% CH₂O--formaldehyde) and adjust the pH of mixture to 8-9. Heat the mixture,maintaining this pH, at reflux until a drop of mixture hydrophobes(precipates) in an excess of 0° C. water. At this point 280 parts byweight of polyvinyl alcohol are added and reaction continued for 40minutes at reflux. The reaction product is then dehydrated, preferablywith vacuum to produce a white fluxible, partially water solubleproduct. From this product, thirty-five parts (by weight) thereof aremixed with 5 parts of Carbowax (as a hot melt processing aid), 1 part ofzinc stearate (lubricant), 1 part of pigment for color and 51 parts ofWollastonite filler (calcium silicate), and 5 parts of water as aprocessing aid. This resin filler mixture is then applied by hot meltprocessing to a glass mat so as to result in an uncured matrix prepregof 90% resin mixture (by weight) and 10% glass mat. The resultant matrixwas then utilized to make a plastic "negative" printing plate by moldingand curing at 325° F. and 100 psi against a magnesium or polyester"master" plate.

When used as a mold insert, the resultant matrix printing plate wasgenerally unsatisfactory as it showed high compressive-setcharacteristics. The letters of the matrix compressed to differentheights when polypropylene printing plates were molded against itthereby providing uneven and blurred printed copies.

While, the invention has been described in conjunction with the use of aglass fiber mat, other forms of mats can be used such as those with thecommon vegetable and mineral fibers. Likewise, while Wollastonite isused as a filler, others can be used as can other lubricants and hotmelt processing aids which are well known. Also, while the cured matrixhas been described in conjunction with its use as a "negative" to formduplicate positive plates, the cured and formed mat may be used directlyas a "positive" printing plate for some applications.

What I claim is:
 1. The method of making printing platescomprising,forming a carrier containing a reactive resin comprising thereaction product of an aminoplast resin and polyvinyl alcohol under heatand pressure against a master printing plate so as to produce a curednegative of said master printing plate, inserting said cured negativeinto a molding device so as to provide a mold insert therein, andflowing a plastic material against said molded negative insert andcuring said plastic to produce a copy of said master printing plate. 2.A method of making printing plates as claimed in claim 1, wherein saidmaster printing plate includes a polyester resin.
 3. A method of makingprinting plates as claimed in claim 1, wherein said master printingplate is magnesium.
 4. A method of making printing plates as claimed inclaim 1, wherein a thermoplastic material is flowed against said moldednegative insert.
 5. A method of making printing plates as claimed inclaim 1, wherein polypropylene is flowed against said molded negative.6. A mold component comprising,a relatively hard plastic sheet having asubstantially homogeneous dense structure with formed areas thereon,said mold having been somewhat porous during its forming to permit gasesto escape therethrough and having a relatively hard surface after itsforming such that the formed areas thereon will take minimalcompressive-set upon the molding thereagainst of a plastic materialunder heat and pressure, said mold component including a reactionproduct of the components of an aminoplast resin and polyvinyl alcohol.7. A negative printing plate against which a plastic material may bemolded under heat and pressure to produce a positive printing platecomprising a reaction product of the components of an aminoplast resinand polyvinyl alcohol in a cured condition on a carrier layer.
 8. Aprinting plate matrix capable of being shaped under heat and pressureand then being used as a part of a mold for imparting a portion of itsshape to a plastic material under heat and pressure comprising,a carrierhaving a porous characteristic, and a curable resin carried by saidcarrier capable of receiving very sharply defined impressions on asurface thereof upon molding and being cured, said surface being able tobe used as a mold against which another plastic material may be shaped,said resin including a reaction product of the components of anaminoplast resin and polyvinyl alcohol.
 9. A printing plate matrix asclaimed in claim 8 wherein said aminoplast is derived from an aminocompound taken from the group consisting of urea, thiourea, cyclicethylene urea, dicyandiamide, melamine and alkyl and aryl melamines. 10.A printing plate matrix as claimed in claim 8 wherein from 0.75 parts to2.6 parts by weight of said aminoplast to 1 part by weight of saidpolyvinyl alcohol are used in making said resin.
 11. A printing platematrix as claimed in of claim 8 wherein said matrix is cured in arelatively flat condition and can then be bent to at least anapproximate 15" diameter of a printing press cylinder.
 12. The printingplate matrix as claimed in claim 8 wherein said aminoplast is melamineformaldehyde.
 13. A printing plate matrix as claimed in claim 8 whereinsaid carrier is a permeable glass fiber mat.
 14. A printing plate matrixas claimed in either of claims 8 or 9, wherein from 1 to 1.5 parts byweight of said aminoplast to 1 part by weight of polyvinyl alcohol areused in making said resin.
 15. A printing plate matrix as claimed inclaims 10 or 11 wherein said polyvinyl alcohol has molecular weight inthe range of 2,000 to 120,000.
 16. A printing plate matrix as claimed inclaim 15 wherein said polyvinyl alcohol has a molecular weight in therange of 2,000 to 14,000.
 17. A printing plate matrix as claimed inclaim 16 wherein said polyvinyl alcohol has a molecular weight in therange of 2,000 to 4,000.
 18. The shaped mold resulting from curing aprinting plate matrix as claimed in claim 8 against a polyestermaterial.
 19. The method of making a molded carrier comprising,reactingthe components of an aminoplast resin with polyvinyl alcohol to producea reaction product, applying the cured reaction product by hot meltprocessing to a somewhat porous carrier and allowing the hot melt tocool, and then pressing said coated carrier against a mold surface andcuring under heat and pressure to produce a hard but somewhat flexiblemolded carrier.